With a global seafood production of about 51.7 million ton in 2006 and an annual growth rate of 6.9% from 1970-2006, aquaculture is one of the fastest growing sectors in the food industry. Feed represents 40-70% of operating costs for aquaculture operations. Fish diets typically contain between 20 and 55% crude protein, depending on the fish species. High quantities of fish meal are commonly used in these feeds to supply fish with essential proteins, amino acids and fatty acids. However, during the last 3 years prices for fish meal have remained above $1000 ton-1 and have even approached $2000 ton-1 in 2010. Increasing expenses and potential declining supplies of fish meal have led scientists to search for less expensive but compatible alternative protein sources for fish feed; most of which are based on animal or plant protein sources. The objective of this study is to review some alternative protein sources including animal byproducts (e.g., poultry byproducts), fishery byproducts, bacterial proteins, plant proteins (e.g., soybean meal, distillers dried grains with solubles and others). The problems and advantages of these alternatives (i.e., nutritive, levels of inclusion and their acceptability values in fish diets) will be discussed.